TABLE III. 



List of the most important differences in Animal Egg-cleavage and 



Gastrnlation.''^ 



The letters a-/ indicate the 6 animal tribes (the primitive animals being 

 excluded) : a, Plant-animals ; h, Worms ; c, Soft-bodied animals {Mollusca) ; 

 d, Star-animals {Echinoderma) ; e, Articulates (Arthropoda) ; /, Vertebrates. 



I. 



Total Cleavage, 



Segmintatio totalis. 



Holoblastic Eggs. 



Gastrula with- 

 out 

 nutritive yelk. 

 Hologaitrula. 



I- Original Cleavage. 



{Scgmentatio primordialis.) 

 Archiblastic eggs. 



Bell-gastrula. 



{Archigastrula.) 



(ri.ite II. Fig. l-G.) 



a. IMost low Plant-animals (low 



Sponges, Ilydrapolyps, Me- 

 dusa-, Corals). 



b. Many low Worms (S igitta, 



Phoronis, Ascidia, many 

 Nematodes, etc.). 



c. A few low Soft-bodied .animals 



(J/bHM.sca)— Terebratula, Ar- 

 giope, Pisidium. 



d. Most Star - animals {Echino- 



derma). 



e. A few low Articul.ites (some 



Branchiopods, Copepods, Tar- 

 digrades). 

 /. The SkuU-Iess Vertebrate (Am- 

 pbioxus). 



11. Unequal Cleava'^e. 



(^Segmentatio inaqnalis.') 

 Amphiblastic eggs. 



Hood-gastrula. 



(^Am.phigastrida.~) 

 (Plate II. Fig. 7-n.) 



a. Numerous Plant-animals (many 



Sponges, Medu^ie, Corals, 

 Siphooopbores, Ctenophorai). 



b. Most ^Vorms. 



c. Most Soft-bodied Animals (Mol- 



lusca). 



d. Individn.al Star-animals (vivi- 



parous species and a few 

 others). 



e. A few low Articulates (^Arthro- 



poda)—\)oVa Crustaceans and 

 Tracheates. 

 /. Cyclostoma, Ganoids, Amphibia, 

 Mammals (all ••). 



II. 



Partial Cleavage. 



Segmentatio partialis. 



Meroblastic eggs. 



Gastrula with 



nutritive yelk. 



Merogastrida. 



in. Discoidal Cleavage. 



{Segmentatio discoidalis.') 



Discoblastic eggs. 



Disc-gastrula. 



{Disco-gastrula.) 



(Plate III. Fig. 18-24.) 



c. Cuttle-fish, or Cephalopods. 



e. Some Articulates (Arthropoda), 

 Millepedes, Scorpions, and 

 others. 



/. Primitive Fishes (^Selachii), 

 Osseous Fishes, Reptiles, 

 Birds (and Monotremes .'). 



IV. Superficial Cleavage. 



(^Segmentatio siqxrjic talis. ) 

 Peribhistic egi;s. 



Bladder-gastr u a. 



(Perigastrua.') 

 (Plate III. Fig. 25-aO.) 



r a. A few Sponges (.'). 

 Alcyonium (:). 



6. Individual Worms (?). 



e. The great m.njority of Articu- 

 lates (.1 rth ropoda) — Crus- 

 taceans, Myriopods, Spiders, 

 Insects. 



